Date: Fri, 12 Dec 2014 10:33:59 -0500 From: John Baldwin <jhb@freebsd.org> To: Mike Gelfand <Mike.Gelfand@logicnow.com> Cc: Konstantin Belousov <kostikbel@gmail.com>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: [BUG] Getting path to program binary sometimes fails Message-ID: <3715296.8JkIjC2VMR@ralph.baldwin.cx> In-Reply-To: <27C465FC-E8C7-44CB-A812-65213BB8AC9F@logicnow.com> References: <91809230-5E81-4A6E-BFD6-BE8815A06BB2@logicnow.com> <2066750.N3TZpYSHCy@ralph.baldwin.cx> <27C465FC-E8C7-44CB-A812-65213BB8AC9F@logicnow.com>
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On Friday, December 05, 2014 03:52:41 PM Mike Gelfand wrote: > On Dec 5, 2014, at 6:19 PM, John Baldwin <jhb@freebsd.org> wrote: > >> No, not NFS but ZFS. Could that be an issue? The FreeBSD 8 machine I > >> mentioned before has UFS. > >> > >> Also, as you can see from the video I recorded (and from the code I > >> provided), path resolution succeeds and fails within fractions of a > >> second > >> after process startup. > > > > Are you seeing vnodes being actively recycled? In particular, do you see > > vfs.numvnodes close to kern.maxvnodes? You can try raising > > kern.maxvnodes. > > If vfs.numvnodes grows up to the limit then as long as you can stomach the > > RAM of having more vnodes around that would increase the changes of your > > paths remaining valid. > > When the call works, sysctl returns: > vfs.numvnodes: 59638 > kern.maxvnodes: 204723 > The times it doesn't, the output is: > vfs.numvnodes: 60017 > kern.maxvnodes: 204723 > I've selected maximum numbers. Monitoring was made with > while sysctl vfs.numvnodes kern.maxvnodes; do sleep 0.1; done > > So it seems that's not related, correct? 60K is much less than 200K. Yes. Unfortunately, we don't expose a raw counter for vnode recycling (I should really add one). I think we might also purge unused vnodes if we have too many "free" vnodes. However, directories that aren't currently open by a process (meaning via opendir()) count as "unused", so are subject to purging. You can try increasing "vfs.wantfreevnodes". Also, please try this patch. It just adds a counter for recycled vnodes. If this value increases during your test then it does show that recycling is occurring. If it doesn't, then that rules it out. Index: vfs_subr.c =================================================================== --- vfs_subr.c (revision 275512) +++ vfs_subr.c (working copy) @@ -156,6 +156,10 @@ static int vlru_allow_cache_src; SYSCTL_INT(_vfs, OID_AUTO, vlru_allow_cache_src, CTLFLAG_RW, &vlru_allow_cache_src, 0, "Allow vlru to reclaim source vnode"); +static u_long recycles_count; +SYSCTL_ULONG(_vfs, OID_AUTO, recycles, CTLFLAG_RW, &recycles_count, 0, + "Number of vnodes recycled"); + /* * Various variables used for debugging the new implementation of * reassignbuf(). @@ -988,6 +992,7 @@ vtryrecycle(struct vnode *vp) __func__, vp); return (EBUSY); } + atomic_add_long(&recycles_count, 1); if ((vp->v_iflag & VI_DOOMED) == 0) vgonel(vp); VOP_UNLOCK(vp, LK_INTERLOCK); -- John Baldwin
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